1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD), and more particularly, to an in-plane switching (IPS) mode LCD and a method of fabricating the same.
2. Discussion of the Related Art
As the performance capabilities of active matrix LCDs rapidly increase, LCDs are being more widely used as flat-type displays in televisions (TVs), portable computers, and monitors. Among active matrix LCDs, a twisted nematic (TN) type LCD is typically used. In the TN-type LCD, electrodes are respectively positioned on two substrates, a director of liquid crystal is arranged to make the director of the liquid crystal have an initial twist angle of 90°, and a voltage is applied to the electrodes to rotate the director of the liquid crystal. The TN-type LCD is favored on the grounds that it provides excellent contrast and color reproducing characteristics.
However, the TN-type LCD has the chronic problem of a narrow viewing angle. To solve the narrow viewing angle problem of the TN-type LCD, an in-plane switching (IPS) mode, where two electrodes are formed on one substrate and a director of a liquid crystal is adjusted by a transverse electric field generated between the two electrodes, has been introduced. A related art IPS mode LCD will be described below.
FIG. 1 is a cross-sectional view of a related art IPS mode LCD. FIG. 2 is a cross-sectional view of a compensation film and a polarization film of the related art IPS mode LCD. FIG. 3 is a schematic view illustrating directions of a polarization axis and liquid crystal in the related art IPS mode LCD.
As shown in FIG. 1, the related art IPS mode LCD includes a color filter array substrate 21, a thin film transistor (TFT) array substrate 11 and a liquid crystal (LC) layer 31 between the color filter array substrate 21 and the TFT array substrate 11. A black matrix layer 22 on the surface of the color filter array substrate 21 prevents light leakage from regions other than the pixel regions. A color filter layer 23, including red, green, and blue filters for reproducing colors, is positioned in respective pixel regions within the black matrix on the surface of the color filter array substrate 21.
Gate lines (not shown) and data lines 15 for defining respective pixel regions are formed on the TFT array substrate 11. TFTs are formed adjacent to where the gate lines and the data lines cross. Common electrodes 24 and pixel electrodes 17 are arranged in an alternately manner on the TFT array substrate 11 for generating a transverse electric field.
The TFT includes a gate electrode 12a branching off from the gate line, a gate insulation film 13 formed over the entire surface of the substrate, including the gate electrode 12a, a semiconductor layer 14 formed on the insulation film 13 that corresponds to the gate electrode 12a, a source electrode 15a formed at one end of the semiconductor layer 14 and a drain electrode 15b branching off from the data line and formed at the other end of the semiconductor layer 14. The pixel electrode 17 is connected to the drain electrode 15b of the TFT via a contact hole passing through a passivation layer 16 so as to receive a data voltage from the TFT. The common electrodes are connected in an integral fashion and provided with a voltage from an external circuit or ground.
The IPS mode LCD has the common electrodes 24 and the pixel electrodes 17 on the same substrate. When a voltage is applied across the two electrodes so as to generate a transverse electric field E, which is horizontal with respect to the substrate, the liquid crystal molecules rotate while maintaining the orientation of the liquid crystal molecules in their horizontal state with respect to the substrate. Alignment layers 30a and 30b are respectively provided on the inner surfaces of the TFT array substrate 11 and the color filter array substrate 21 to initially align the liquid crystal molecules in the liquid crystal layer 31.
A first polarization film 53 and a second polarization film 54 are respectively attached to the outer surfaces of a liquid crystal (LC) panel 50, which includes the two substrates and the liquid crystal layer 31, to transmit only light of a polarization plane in a predetermined direction. An A-plate compensation film 52 and a C-plate compensation film 51 are further provided between the second polarization film 54 and the liquid crystal panel 50 to compensate for a phase change of light due to an inadequate viewing direction. The compensation film and the polarization film of the IPS mode LCD will be described in detail with reference to FIG. 2.
The C-plate compensation film 51 and the A-plate compensation film 52 are further provided at one side of the IPS mode LC panel 50, as shown in FIG. 2. The C-plate compensation film 51 is made of a liquid crystal material having a positive dielectric constant to compensate for a phase in a vertical direction. The A-plate compensation film 52 is made of a liquid crystal material having a negative dielectric constant to compensate for a phase in a horizontal direction. As described above, the IPS mode LCD compensates for the phase using a biaxial film or two compensation films of the A-plate compensation film and the C-plate compensation film.
The first polarization film 53 and the second polarization film 54 are attached to the outermost portions of the LC panel 50, respectively. The first polarization film 53 and the second polarization film 54 are flexible-type films and made of a multilayer film, such as triacetate cellulose (TAC) films, poly vinyl alcohol (PVA) films, protection films, and releasing films. These polarization films transmit only light having a polarization plane in one predetermined direction from natural light, which has polarization planes in all directions of 360°, and absorbs the rest of the light to provide polarized light.
The A-compensation film 52 and the C-compensation film 51 are a coated type and can be formed by coating and hardening the material on the outer or inner surface of the LC panel 50. The C-plate compensation film 51 is coated and hardened on the surface of the LC panel 50, the A-plate compensation film 52 is coated and hardened on the C-plate compensation film 51, and finally, the second polarization film 54 is attached on the A-plate compensation film 52 and the first polarization film 53 is attached on the LC panel at the opposite side. The first polarization film 53 and the second polarization film 54 are attached to the outermost portions of the LC panel 50 and compensation films, by removing releasing film from adhesive sides on the polarization films and applying the adhesive sides of the polarization films to the LC panel 50.
As shown in FIG. 3, the direction of a polarization axis of the second polarization film 54 is set in a direction perpendicular to an alignment direction of the liquid crystal layer 31. The direction of a polarization axis of the first polarization film 53 is set in a direction parallel with an alignment direction of the liquid crystal layer 31.
The above-described IPS mode LCD has the following problems. First, since the compensation film is additionally provided to the LCD, it is difficult to manufacture an LCD with a lightweight and slim profile. Further, time and cost are consumed due to the process of adding the compensation film. Second, when the polarization film is attached to a final product, the releasing film and the protection film of the polarization film should be removed. During the process of removing those films, layers of the multilayer film that has been attached can be exfoliated due to their weak adhesion.